Modding Help Need help with editing and creating custom maps!

So I've been working on this custom NPC for about 6 months. I haven't gotten around to finishing it because I really need help getting a custom map for him. I want to try editing the town, and placing his house right there. Or adding a new map you can enter from the Bus Stop.

Can somebody maybe give me a rundown of how coding works for editing and creating maps? I've been looking through different tutorials and files from different maps, and I'm honestly too much of a rookie to figure this out on my own lmao.

Make sure you're not using any immersive mods like SVE or Karmylla's. Something tells me that your mod wouldn't work with those types of mods. Alternatively, you can just try something else- some things are just too hardcoded to work around even with modding tools such as Tiled.